Solution-Processed Bulk Heterojunction Solar Cells with Silyl End-Capped Sexithiophene

Abstract

We fabricated solution-processed organic photovoltaic cells (OPVs) using substituted two sexithiophenes, a,w-bis(dimethyl-n-octylsilyl)sexithiophene (DSi-6T) and a,w-dihexylsexithiophene (DH-6T), as electron donors, and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor. Solution-processed OPVs usingDH-6TandDSi-6Tshowed good photovoltaic properties in spite of their poor solubility. The best performance was observed onDSi-6T : PCBM 1 : 5 (w/w) blend cell with an open circuit voltage (Voc) of 0.63 V, short circuit current density (Jsc) of 1.34 mA/cm2, fill factor (FF) of 55%, and power conversion efficiency of 0.44% under AM 1.5 G illumination. AlthoughDH-6Thas higher hole mobility thanDSi-6T, theDSi-6T : PCBM blend cell showed higher hole mobility thanDH-6T : PCBM cell. Therefore,DSi-6Tcell showed higher device performance thanDH-6Tcell due to its silyl substitutions, which lead to the increase of the solubility. The incorporation of solution-processed TiO2interfacial layer in theDSi-6T : PCBM devices significantly enhances FF due to the reduced charge recombination near active layer/Al interface.

Understanding the open circuit voltage in organic solar cells on the basis of a donor-acceptor abrupt (p-n++) heterojunction

“…The HOMO D energy for each polymer or small molecule was taken from Refs. Hellstrӧm et al (2009), Thompson and Frechet (2008), Li et al (2010), Tang et al (2006), Choi et al (2013). The calculated barriers and the numerical values employed in the calculations are listed in Table 1.…”

“…(3) Φ b (eV) Diff. Φ b (eV) V 0C (V) Jsc (mA•cm −2 ) n HOMO D (eV)/Literature Weight ratio (upper four)/Thicknesses (lower two) LPPP5:PCBM 1 1.03 0.73 4.5 1.53 5.3 Hellstrӧm et al (2009) (1:3) MDMO:PCBM 1.1 1.14 0.83 3.4 1.45 5.4 Thompson and Frechet (2008) (1:4) APFO3:PCBM 1.2 1.21 1.02 4.5 1.56 5.5 Li et al (2010) (1:4) Pc/C 60 0.85 0.91 0.45 5.6 1.6 5.1 Tang et al (2006) 40 nm/30 nm 6T/C 60 0.82 0.87 0.41 2.3 1.7 5.1 Choi et al (2013) 40 nm/80 nm understand such a rule by considering Fermi level alignment of the nonintentionally doped semiconductors in the three OBHJ junctions including the internal donor-acceptor heterojuntion which corresponds to an abrupt (p-n ++ ) heterojunction.…”

Efficient planar heterojunction based on α-sexithiophene/fullerene through the use of MoO3/CuI anode buffer layer

“…Moreover, PHJ configuration simplifies the interface geometry, which permits to study more easily the chemical and physical interactions between the stacked layers [7] In the last few years oligothiophene family, α-sexithiophene (-6T) in particular, has gotten much attention for different applications such as organic field effect transistors, light emitting diodes [8] [9] [10] and as donor material in organic solar cells because of its high hole mobility [11], reasonable absorbance in the visible range, high purity, simple synthesis and easy chemical modification by changing the number of thiophene rings [3] [12]. Actually, the maximum power conversion efficiency (PCE) of 8.4% was achieved using three-layer PHJ device structure, where, -6T was the principle donor material [13].…”